In semiconductor technology, substrates are generally back-thinned to reduce the dimension of the components which are being formed. One of the most frequent reasons for the use of back-thinning is to produce electrically conductive interconnections through the substrate. These lines are called through silicon via (TSVs) in particular due to their frequent use in silicon substrates. Since the industrially produced substrates, in particular wafers, have a thickness of more than 500 μm, and the TSVs however only have a length of roughly 100 μm, it is necessary to remove the residual parts of the substrate. At the end of the back-thinning process a function wafer with a thickness as small as possible will result. The thickness depends on the technical and electrical properties.
The product substrates are fixed on carrier substrates so that they are stabilized during and mainly after the back-thinning process. Mainly semiconductor substrates or glass substrates are used as carrier substrates.
The product substrates are subjected to various processes after bonding to the carrier substrate. In particular, functional units, for example MEMs, microchips, memory units etc. are formed on the product substrates.
After back-thinning and other processes, the product substrate must be detached from the carrier substrate in order to be able to be further processed.
The process of fixing is called bonding. If the fixing is limited in time, it is temporary bonding. For temporary bonding various materials are used which enable fixing of the two substrates during the different process steps, but on the other hand allow a separation of the substrates with certain chemical and physical effects. The cement bonds between the product substrate and carrier substrate can for example be chemically broken. Another method is the separation of the substrates by the action of heat and the application of a shearing and/or normal force. A further method includes destroying the cement by electromagnetic radiation, especially by UV light. To do this, at least one of the two substrates must be transparent to the UV light.
All these hitherto known methods have major defects which can lead to an at least partial adverse effect on the properties of the interconnect layer and/or the substrates or components which are located thereon.
In debonding/detachment of the carrier substrate from the product substrate, a host of critical factors must be considered and a top priority includes exposing the brittle product wafer which is very expensive due to preprocessing to as little stress as possible and not damaging it. The detachment of the first substrate should on the other hand proceed economically and quickly with as little energy expenditure as possible. In a plurality of known detachment processes it is necessary, especially for dissolving the adhesion properties of the adhesion layer between the wafers, to heat the stack composed of the carrier wafer and structure wafer/product wafer to a temperature which is specific to the cement.